Design limits of electric motors?

[John Larkin]

On Tue, 8 Jun 2004 14:24:49 +0300, "Tzortzakakis Dimitrios"
<dimtzortihatespam@nospamotenet.gr> wrote:

Are you joking?GEARED?Steam turbine?They are on a single-cast shaft.THAT
shaft is expensive, thus it connects the turbine and generator.Imagine a
gear for 2,500,000 hp (usual power of a nuclear plant generator).The
generator and turbine are designed to run at the same speed.Even train
locomotives use diesel-electric transmission, and the traction motors are
directly coupled on the wheels.So must be happening at the ships, too.

I was referring to a steamship. Prop RPMs are in the 100 range, the
small high-pressure turbine spins maybe 12 grand - it makes 80% of the
power - and the huge LP turbine runs roughly three or four. The main
bull gear is typically about 30 feet in diameter or so... I saw one
being ground at DeLaval, and I designed a number of steamship throttle
control systems. The LASH ships I worked on made 32,000 shaft
horsepower at 120 RPM. If the prop falls off, there's a good chance
the turbine will disintegrate.

Direct-coupled reversing diesels are popular in ships nowadays because
they are simpler and more compact than a high-efficiency steam plant.
I think the steam plants are still more efficient, and the stuff they
burn - essentially asphalt - is nasty and dirt cheap.

John

 

[John Larkin]

On Tue, 8 Jun 2004 14:19:33 +0300, "Tzortzakakis Dimitrios"
<dimtzortihatespam@nospamotenet.gr> wrote:

It depens on number of poles.(for asynchronous motors).
Double pole->3000 rpm (at 50 Hz) ->3600 rpm (at 60 Hz) 4 pole->1500 rpm or
1800 rpm.

A DC motor, either series, shunt or compound excitation runs at about the
same speed.Or slower, of course.

My Dremel tool has a series-wound brush motor, and runs at 30,000 or
so.

John

 

[Tim Wescott]

Mjolinor wrote:

"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:10ca1lobqqlio8d@corp.supernews.com...

--snip--
I believe that the OP wasn't going to spin the turbine to spin a prop,
he was more interested in spinning the turbine to drive the aircraft.

In theory a high-bypass fanjet motor could produce pretty much the same
thrust if you spun the fan with an electric motor as with it's built-in
turbine engine, and you'd get the same kinds of high-speed efficiency
gains that you do from using a fanjet.

The real rub would be that "infinite source of electrical power" -- so
far the only thing that really beats hydrocarbon fuels for power density
is atomics, and while the US was crazy enough to seriously investigate
atomic-powered craft in the 50's that would stay up for days they
weren't crazy enough to continue the experiment once they developed
intercontinental missiles. Even there they were going to use hot air
from the reactor to drive the turbines; the weren't going to generate
electricity then use motors.

--


I can't understand this conversation, surely an aerofoil shaped bladed rotor
would achieve the same whether it was inside a tube or outside it. If you
dont have significantly higher pressure gas on one side of the blade then
you will reach a speed where the effect is to create vacumn on the "high
pressure side" rather than pressure increase at the back side (similar to
cavitation on a water propellor), this will still create small ammounts of
thrust I suppose but it would pretty quickly reach a maximum that you
couldn't get past.

Even if I visualise the pressures in a thing with 10 or more rotors with
different pitch (shaped) blades I can't see how it would work at all. I end
up back at one "screw" pulling or pushing it's way through the air with all
the limitations that standard propellors have. Enlighten me please.

A turbofan engine (which is used by most airliners these days) gets most
(about 80% IIRC) of it's thrust from the fan and about 20% from the
turbine engine buried inside of it.

Ducted fans are used because a the tips of a large, fast propeller
exceed the speed of sound and ruin the propeller efficiency. A
relatively small-diameter prop with lots of blades ends up throwing a
lot of air radially off its travel path. The answer is to put a
multi-bladed propeller into a tube, and turn it with a turbine engine -
that's a turbo fan.

So if you take that turbofan engine and replace it's turbine section
with a big-ass electric motor you'll get almost as much thrust as
before, but on electric power instead of kerosene.

Note that none of this applies to low-bypass engines, like the ones used
in older jet fighters and the concord: Those engines get _all_ of their
thrust directly from the hot, fast exhaust. It's great for supersonic
flight because the exhaust is going so very fast, but for slower travel
it's not good for fuel efficiency because a lot of air moving slowly
produces more thrust than a little bit of air moving fast.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Tim Wescott]

DaveC wrote:

On Tue, 8 Jun 2004 06:40:33 -0700, DaveC wrote
(in article <0001HW.BCEB0FE10039AEFDF03055B0@news.individual.net&gt:


So, basically, turning a fan in a tube (spinning a turbojet engine without
fuel) doesn't gain you much efficiency. If electrics are to power an
aircraft, it seems that an efficient propeller is the best that you can do.


And then hi rpms isn't important any more. Indeed, since torque doesn't
increase with speed (I *do* have that fact right, don't I?), gearing isn't
necessary and propellers have a relatively low maximum speed requirement.

Your electric motor will probably be most efficient at speeds higher
than want to drive your prop -- so you'll still want to gear the motor
down to the prop.

And I disagree about the turbofan assertion -- assuming that you've got
the motor to do it, if you want to fly at jetliner speeds a propeller is
going to be horribly inefficient, which is why jetliners use turbofans
and not turboprops. Since only 20% or so of the thrust of a turbofan is
from the turbine I think you _could_ use a motor, keeping in mind that
it's going to be a _long_ time before this is a better solution than
just burning jet fuel in a turbine!

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[John Larkin]

On Tue, 8 Jun 2004 14:31:09 +0300, "Tzortzakakis Dimitrios"
<dimtzortihatespam@nospamotenet.gr> wrote:

GEARED down?I have seen a WWII airplane engine, and the crankshaft is
directly coupled to the propeller.The jet engines are ~2500 hp, so it's
impossible to gear.The pilot controls only the fuel supply.

The single-engine VTOL Joint Strike Fighter runs a shaft fore-aft,
from the engine to the front lift fan, which blows down. There is
right-angle gearing at the fan casing. They shoot 32,000 horsepower
down this shaft; there's a clutch somewhere, too. They're using my VME
arbitrary waveform generators to simulate all the sensor inputs (shaft
speed, torque, displacements) into the control computers now being
designed.

Most jet engines have internal gearing. Jet helicopters obviously have
gears.

John

 

[Winfield Hill]

John Larkin wrote...

Tzortzakakis Dimitrios wrote:

GEARED down?I have seen a WWII airplane engine, and the crankshaft
is directly coupled to the propeller.The jet engines are ~2500 hp,
so it's impossible to gear.The pilot controls only the fuel supply.

The single-engine VTOL Joint Strike Fighter runs a shaft fore-aft,
from the engine to the front lift fan, which blows down. There is
right-angle gearing at the fan casing. They shoot 32,000 horsepower
down this shaft; there's a clutch somewhere, too. They're using my
VME arbitrary waveform generators to simulate all the sensor inputs
(shaft speed, torque, displacements) into the control computers now
being designed.

Most jet engines have internal gearing. Jet helicopters obviously
have gears.

What happens when a tooth breaks? I suppose there's a mandatory
replacement schedule. What's a typical mandated gear life?

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)

 

[daestrom]

"DaveC" <me@privacy.net> wrote in message
news:0001HW.BCEA9AA7001E357EF03055B0@news.individual.net...

On Mon, 7 Jun 2004 15:08:58 -0700, Jon Elson wrote
(in article <40C4E77A.1040405@artsci.wustl.edu&gt:

just a few revolutions. Very stiff structures can tolerate a rapid
acceleration
through the first critical speed, and then operate safely above that
speed.
But, getting a machine to tolerate that speed, even for a moment, is
quite
tricky. The other problem is ball bearings, for the most part, can't
handle
100,000 + RPM. At the least, they need continuous oil mist cooling to
remove

But what about conventional (fuel) turbine engines. Surely they turn in
the
100,000 rpm range, and use ball bearings.

Actually, I think you'll find the high speed shafts are in journal bearings.
And they have a continuous supply of oil, pumped by an oil pump driven from
an auxilary shaft. The aux shaft is at right-angle to the main shaft and
driven by bevel gearing at a slower speed.

daestrom

 

[daestrom]

"Tzortzakakis Dimitrios" <dimtzortihatespam@nospamotenet.gr> wrote in
message news:ca47nd$ehr$1@usenet.otenet.gr...

Are you joking?GEARED?Steam turbine?They are on a single-cast shaft.THAT
shaft is expensive, thus it connects the turbine and generator.Imagine a
gear for 2,500,000 hp (usual power of a nuclear plant generator).The
generator and turbine are designed to run at the same speed.Even train
locomotives use diesel-electric transmission, and the traction motors are
directly coupled on the wheels.So must be happening at the ships, too.

Hate to burst your bubble, but they *do* make gearing for this kind of
power. Typical steamships use reduction gears between the IP/LP turbines
(in thousands of RPM) and the main shaft (hundreds of RPM). And smaller
gearing between the HP and IP turbines. Bull-gears, the final output gear
connected to the propeller shaft are large with double helix cut. Often use
double-reduction with 'quill' shafts between successive gear stages.

Saw more than one bull gear get some broken teeth ground out. Didn't
replace the teeth, just ground down the sharp edges so they wouldn't wear
into the low-speed pinions (some sailors didn't believe the rules about
FOD). Some marine applications include clutches that can carry over 35000
hp. These ain't your standard automobile clutch, they have dozens of
friction plates and positive, splined-sleeve engagement.

Large stationary power plants have the HP and LP turbines co-linear with the
generator, that is true. But the 'shaft' is made up of several pieces, one
for each turbine section and another for the generator. Each section is
bolted to the next with flat-faced, bolted couplings. One plant (I think in
Korea) a year or so back had a failure where a fire in one bearing support
caused it to sieze. The shaft twisted right apart and in the process threw
pieces/parts all around the turbine building. The pictures were *very*
impressive.

Get a couple of mechanical engineers together in a room and they can come up
with things almost as outlandish and exotic as any EE's

daestrom

 

[Mjolinor]

Get a couple of mechanical engineers together in a room and they can come
up
with things almost as outlandish and exotic as any EE's

And from the EE side we have the Rabbit phone
For the mechanics we have the Edsel.

And as proof that the engineers can get it right but still not succeed there
is of course Betamax.

 

[daestrom]

"John Larkin" <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in
message news:4imbc094fqn5i53fvm0gkqdr8o2h3r0fss@4ax.com...

On Tue, 8 Jun 2004 14:19:33 +0300, "Tzortzakakis Dimitrios"
dimtzortihatespam@nospamotenet.gr> wrote:

It depens on number of poles.(for asynchronous motors).
Double pole->3000 rpm (at 50 Hz) ->3600 rpm (at 60 Hz) 4 pole->1500 rpm
or
1800 rpm.

A DC motor, either series, shunt or compound excitation runs at about the
same speed.Or slower, of course.

My Dremel tool has a series-wound brush motor, and runs at 30,000 or
so.

One of the drawbacks/precautions about series-wound DC motors is that if
they are unloaded, the only thing limiting their speed is the windage and
friction losses. Some can literally tear themselves apart if run unloaded.
Of course, your Dremel is designed *not* to do that. Some older automobile
starters have been destroyed by running them on the bench to the point where
the copper bars come out of the rotor slots.

daestrom

 

[John Larkin]

On 8 Jun 2004 10:45:08 -0700, Winfield Hill
<Winfield_member@newsguy.com> wrote:

John Larkin wrote...

Tzortzakakis Dimitrios wrote:

GEARED down?I have seen a WWII airplane engine, and the crankshaft
is directly coupled to the propeller.The jet engines are ~2500 hp,
so it's impossible to gear.The pilot controls only the fuel supply.

The single-engine VTOL Joint Strike Fighter runs a shaft fore-aft,
from the engine to the front lift fan, which blows down. There is
right-angle gearing at the fan casing. They shoot 32,000 horsepower
down this shaft; there's a clutch somewhere, too. They're using my
VME arbitrary waveform generators to simulate all the sensor inputs
(shaft speed, torque, displacements) into the control computers now
being designed.

Most jet engines have internal gearing. Jet helicopters obviously
have gears.

What happens when a tooth breaks? I suppose there's a mandatory
replacement schedule. What's a typical mandated gear life?

Gosh, I don't know. I'd imagine the stress levels are pretty high.
Helicopters in particular are suicide machines. I've seen some of the
big fanjets disassembled, and they have a 4-foot wide, several inch
thick wrapping of epoxy-kevlar around the main (12 foot diameter) fan
blades to catch them if the rotor disintegrates. They actually test
this, and I'd love to see one of those tests.

This aerospace stuff looks like fun, and it is if you get to see it
but don't have to actually do it. My son-in-law works for Sandia, and
does some explosives stuff. I commented that it must be fun, and he
said, no, after all the management and paperwork and safety measures
and planning and stuff, it's not fun any more.

John

 

[John Larkin]

On Mon, 7 Jun 2004 22:20:23 -0700, DaveC <me@privacy.net> wrote:

On Mon, 7 Jun 2004 15:08:58 -0700, Jon Elson wrote
(in article <40C4E77A.1040405@artsci.wustl.edu&gt:

just a few revolutions. Very stiff structures can tolerate a rapid
acceleration
through the first critical speed, and then operate safely above that speed.
But, getting a machine to tolerate that speed, even for a moment, is quite
tricky. The other problem is ball bearings, for the most part, can't handle
100,000 + RPM. At the least, they need continuous oil mist cooling to
remove

But what about conventional (fuel) turbine engines. Surely they turn in the
100,000 rpm range, and use ball bearings.

Big commercial jets are in the 12K RPM range, and I think some of the
military engine parts spin up to maybe 18K. There are some tiny jet
engines (coke-can size, or smaller) that run around 100K or more.
Research microturbines are pushing something like 500K.

Some steam turbines run in the teens, and they use plain
pressurized-oil bearings, not ball bearings.

John

 

[John Larkin]

On Tue, 08 Jun 2004 21:03:37 GMT, "daestrom"
<daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:

Hate to burst your bubble, but they *do* make gearing for this kind of
power. Typical steamships use reduction gears between the IP/LP turbines
(in thousands of RPM) and the main shaft (hundreds of RPM). And smaller
gearing between the HP and IP turbines. Bull-gears, the final output gear
connected to the propeller shaft are large with double helix cut. Often use
double-reduction with 'quill' shafts between successive gear stages.

Saw more than one bull gear get some broken teeth ground out. Didn't
replace the teeth, just ground down the sharp edges so they wouldn't wear
into the low-speed pinions (some sailors didn't believe the rules about
FOD).

There was a gear being ground at DeLaval for a LASH ship, and the
grinder operator guy set the final grind pass to 10 mils instead of 1
mil. So this 32 foot diameter double-helix million-buck gear came out
with square edges on all the teeth. They called the shipyard
(Avondale), told them the gear would be a few weeks late, and gave the
guy a file. True story.

John

 

[Tim Auton]

"Mjolinor" <mjolinor@hotmail.com> wrote:

Get a couple of mechanical engineers together in a room and they can come
up
with things almost as outlandish and exotic as any EE's

And from the EE side we have the Rabbit phone

Nothing wrong with the electronics in a Rabbit phone was there?
Perhaps there was, but that's not why it failed. It was just a crap
idea. So now they're doing it again with Wi-Fi hotspots.


Tim
--
Love is a travelator.

 

[Mjolinor]

"Tim Auton" <tim.auton@uton.[groupSexWithoutTheY]> wrote in message
news:42ccc0dm8t9j4mr4cvjl2r9qu915jlckrv@4ax.com...

"Mjolinor" <mjolinor@hotmail.com> wrote:

Get a couple of mechanical engineers together in a room and they can
come
up
with things almost as outlandish and exotic as any EE's

And from the EE side we have the Rabbit phone

Nothing wrong with the electronics in a Rabbit phone was there?
Perhaps there was, but that's not why it failed. It was just a crap
idea. So now they're doing it again with Wi-Fi hotspots.

True, it was the application that sucked so remove that one

 

[Don Pearce]

On 8 Jun 2004 10:45:08 -0700, Winfield Hill
<Winfield_member@newsguy.com> wrote:

John Larkin wrote...

Tzortzakakis Dimitrios wrote:

GEARED down?I have seen a WWII airplane engine, and the crankshaft
is directly coupled to the propeller.The jet engines are ~2500 hp,
so it's impossible to gear.The pilot controls only the fuel supply.

The single-engine VTOL Joint Strike Fighter runs a shaft fore-aft,
from the engine to the front lift fan, which blows down. There is
right-angle gearing at the fan casing. They shoot 32,000 horsepower
down this shaft; there's a clutch somewhere, too. They're using my
VME arbitrary waveform generators to simulate all the sensor inputs
(shaft speed, torque, displacements) into the control computers now
being designed.

Most jet engines have internal gearing. Jet helicopters obviously
have gears.

What happens when a tooth breaks? I suppose there's a mandatory
replacement schedule. What's a typical mandated gear life?

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)

They take sonic signatures with built-in transducers of the new
installations. They then listen periodically to see what has changed.
An FFT will reveal where in the gear chain the wear is happening, and
with some experience on the part of the operator, how bad it is. The
parts are changed on the basis of the results.

For carbon fibre parts the situation is different. The parts are
stressed severely to a degree that uses about one third of their
useful life. The remaining two thirds are then very accurately
predictable, and bits don't get changed until they really need to.

d
Pearce Consulting
http://www.pearce.uk.com

 

[daestrom]

"John Larkin" <jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote in
message news:ffbcc05ve9uk2ontedeodbqr775pvall0l@4ax.com...

On Tue, 08 Jun 2004 21:03:37 GMT, "daestrom"
daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:


Hate to burst your bubble, but they *do* make gearing for this kind of
power. Typical steamships use reduction gears between the IP/LP turbines
(in thousands of RPM) and the main shaft (hundreds of RPM). And smaller
gearing between the HP and IP turbines. Bull-gears, the final output
gear
connected to the propeller shaft are large with double helix cut. Often
use
double-reduction with 'quill' shafts between successive gear stages.

Saw more than one bull gear get some broken teeth ground out. Didn't
replace the teeth, just ground down the sharp edges so they wouldn't wear
into the low-speed pinions (some sailors didn't believe the rules about
FOD).

There was a gear being ground at DeLaval for a LASH ship, and the
grinder operator guy set the final grind pass to 10 mils instead of 1
mil. So this 32 foot diameter double-helix million-buck gear came out
with square edges on all the teeth. They called the shipyard
(Avondale), told them the gear would be a few weeks late, and gave the
guy a file. True story.

I believe it. When you screw up something *that* big and expensive, they
find a way to make it work anyway ;-)

daestrom

 

[Rich Grise]

"Mjolinor" <mjolinor@hotmail.com> wrote in message
news:%2exc.1728$WM3.57@newsfe6-gui.server.ntli.net...

To me the only difference between a jet engine and a rocket engine is that
the jet is the most complicated one way valve immaginable so that the
explosion is directed out the back but one of the two components for
combustion can still get in the front. Maybe I am looking at it wrong as I
know less about aviation than I do about electronics . So with my view
in
mind how is an electric motor going to replace some/all of the jet engine
or
is my understanding wrong.

Yeah, you're right. A fan has inherent limitations; a jet adds energy
to the fluid stream - so, since we've got an infinite supply of energy,
drive the compressor part of a jet motor with the Electric Motor and
replace the combustion chamber with a refractory heater that's arbitrarily
hot, to expand the gas. Then lose the turbine, since we've got the
infinite battery.

Cheers!
Rich

 

[Ian Buckner]

"Winfield Hill" <Winfield_member@newsguy.com> wrote in message
news:ca4tv4012vq@drn.newsguy.com...

John Larkin wrote...

Tzortzakakis Dimitrios wrote:

GEARED down?I have seen a WWII airplane engine, and the
crankshaft
is directly coupled to the propeller.The jet engines are ~2500
hp,
so it's impossible to gear.The pilot controls only the fuel
supply.

The single-engine VTOL Joint Strike Fighter runs a shaft fore-aft,
from the engine to the front lift fan, which blows down. There is
right-angle gearing at the fan casing. They shoot 32,000
horsepower
down this shaft; there's a clutch somewhere, too. They're using my
VME arbitrary waveform generators to simulate all the sensor
inputs
(shaft speed, torque, displacements) into the control computers
now
being designed.

Most jet engines have internal gearing. Jet helicopters obviously
have gears.

What happens when a tooth breaks? I suppose there's a mandatory
replacement schedule. What's a typical mandated gear life?

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)

I watched a programme on the development of the JSF. The comment

made was that the front lift fan is only used during vertical landing,
and if anything broke you were going to have "a _really_ bad day".

Regards
Ian

 

[N. Thornton]

andrew@cucumber.demon.co.uk (Andrew Gabriel) wrote in message news:<ca4fi2$aug$1@new-usenet.uk.sun.com>...

In article <MPG.1b2f7b6332df44db98971e@news3.prserv.net>,
krw <krw@att.biz> writes:

DC, or universal, motors can run much faster (add a zero). As I posted
earlier, it's not uncommon for a router (woodworking tool) to have a
no-load speed of 25,000RPM or more.

Universal motors from washing machines (that's european style washing
machines) initially look like a good bet if you're after a mains
motor. However, with no load and without their servo control, they can
get to speeds where they fly to pieces.

This isnt too hard to work round though - but of course that does add
complication. Reduced voltage, dummy loading, monitoring the tacho
output, and designing to avoid no-loads can all work.

Regards, NT